This invention relates to a control valve for a modulator used in a vehicle for an adaptive braking system.
Adaptive braking systems require a modulator which is responsive to control signals generally generated by an electronic control unit upon sensing an incipient skidding condition of the vehicle. The modulator is responsive to output signals from the electronic control units to decay braking pressure when the incipient skidding condition is sensed and to terminate the brake pressure decay and initiate a brake pressure build when the incipient skidding condition no longer exists. Most existing adaptive braking modulators are operated by a fluid motor including a differential pressure responsive piston. Both sides of the piston in existing modulators are normally communicated with engine manifold vacuum when an incipient skidding condition does not exist, but upon generation of the control signal from the electronic control unit indicating existence of an incipient skidding condition, one side of the pressure differential responsive piston is communicated to atmospheric air, thereby urging the latter in a direction releasing the brake pressure of the vehicle's brakes. While this type of modulator works quite well, the rather limited vacuum available in existing automobile engines limits the force which can be generated by the pressure differential responsive piston. Since, particularly in larger vehicles, these modulators cannot generate sufficient brake pressure decay rates, it is necessary to significantly increase the capacity of the modulator.